BS EN IEC 62961:2018 pdf free.Insulating liquids – Test methods for the determination of interfacial tension of insulating liquids – Determination with the ring method.
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3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 862 and the following apply.
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3.1 interfacial tension tension at the interface between two phases
Note 1 to entry: The SI unit of interfacial tension is the Newton per metre (N/m). In practice, the submultiple millinewton per metre (mN/m) is used.
4 Principle
The maximum force, F, necessary to pull or to force a ring of perimeter πD out of the interface between insulating liquid and water in the direction of the insulating liquid is measured. The interfacial tension, σ, is obtained by calculation, where the following approximate equation (1) serves as the base:
is the interfacial tension expressed as mN/m;
is the maximum force exerted on the ring when pulled out of the liquid, in mN;
is the mean diameter of the ring, in m;
is a correction factor， taking into account that the measured maximum force includesthe additional volume of liquid extracted together with the ring because of the finitediameter of the wire and of the lamella overlap inside the ring immediately prior todetachment. Extrapolation formulae have been reported by Zuidema and Waters [5]and others.
To obtain exact values for surface or interfacial tension,it is necessary to measure themaximum force on pulling the ring out of the liquid.Because of the great risk of detachment inthe case of the manual apparatus，extremely smooth manipulation is necessary since thevalue obtained immediately prior to detachment of the film is not identical to the maximumvalue.Automatic tensiometers can determine the maximum value electronically and reversethe platform movement promptly prior to detachment of the film. This makes it possible toobtain reliable,accurate time-consistent serial measurements without tearing the film.
5 Apparatus
5.1Tensiometer
The tensiometer shall be designed for a ring and shall consist mainly of two parts:
support for the sample vessel in the form of a small horizontal platform which can bemoved up and down;
apparatus for measuring the force exerted on the ring; the uncertainty of measurementshall not exceed ±10-6 N, which corresponds to a maximum error of ± 0,1 mg weightmeasurement.
Instead of a torsion balance as stated in ASTM D971,a lever balance or an electronicbalance (laboratory, analytical or microbalance) can be used.To obtain higher efficiency andreproducibility， it is recommended to use an automatic tensiometer incorporating a balancemotor driven platform and evaluation unit.BS EN IEC 62961 pdf download.